Write a calculation by hand, press a key, and get the mistaken step marked on the page. Penmentor, by Abdullah Alhariri, connects a pen-tablet workflow in Xournal++ to Claude Code, Codex or Antigravity.

It aims to give hints before answers and can turn a selected expression into an interactive Manim illustration. The attached 45-second scripted walkthrough uses a fixed model response to demonstrate that workflow; it is not a live accuracy test.

The current setup targets Linux/X11, especially i3, and uses an AI agent you already have configured. A visual correction is still something to check, rather than a guarantee that the maths is right.

Source, setup and original demo:
github.com/AbdullahAlhariri/penmentor